Keep each letter together
Associate pages with their envelope and record the existing order. Make a working copy before rearranging a bundle. A loose page may belong to a different letter than the one beside it.
Compare several dates
Record the written date, postmark and references to events separately. A later reader’s annotation is not equivalent to the author’s date. Mark conclusions that depend on an assumed order.
Leave room for privacy
Letters may discuss living people or matters intended for a limited audience. A timeline can record that correspondence exists without reproducing it. Agree on a sharing boundary before uploading the collection.
Further reading
For source material and collection context, visit US National Archives: family research. Check the collection’s own scope and access instructions before relying on it.